Up to now, a piezoelectric valve which is used to control the inflow and outflow of the fluid or the flow rate is disclosed in U.S. Pat. No. 5,628,411, for example. As shown in FIG. 13, this piezoelectric valve 1 is configured so that a diaphragm 3 whereon a piezoelectric element 2 is provided can be brought near or separated from a valve seat 5 of an output port 4. In this case, if the pressure of compressed air is introduced into a pressure chamber 6 from an input port 7 is P, a force Fp applied to the output port 4 is expressed by: EQU Fp=.pi./4.times.D.sup.2.times.P
(D:Diameter of opening of output port 4). PA1 (k.sub.1 : Spring constant) PA1 a piezoelectric element which is provided on one surface of the diaphragm, and displaces the diaphragm; PA1 a cushioning member which is opposed to the piezoelectric element, and provided on a housing forming the diaphragm chambers; and PA1 a valve seat which is provided for an output port opening in the housing, and wherewith the other surface of on the diaphragm can be contacted; PA1 wherein, when no drive power is applied to the piezoelectric element, the diaphragm is contacted with the valve seat with no elastic energy being built up therein for closing up the output port. PA1 piezoelectric elements which are provided on the diaphragms, respectively, and displace the diaphragms; and PA1 valve seats which are provided for a plurality of output ports opening in a housing forming the diaphragm chambers, and wherewith the diaphragms can be contacted, respectively, wherein: PA1 when no drive power is applied to the piezoelectric elements, the diaphragms are contacted with the valve seats with no elastic energy being built up in the diaphragms for closing up the output ports, and by selectively or simultaneously displacing the plurality of diaphragms, the fluid being selectively or simultaneously introduced to the plurality of output ports.
On the other hand, a recovering force Fs of the diaphragm 3 when the diaphragm 3 is displaced by an amount of displacement of x.sub.1 to close up the output port 4 is expressed by:
Fs=k.sub.1.times.x.sub.1
And, with this piezoelectric valve 1, by setting the pressure P of the compressed air so that Fp=Fs, a closed state is maintained.
On the other hand, when the output port 4 is to be opened, drive power is applied to the piezoelectric element 2 to change the amount of bending of the piezoelectric element 2 for separating the diaphragm 3 from the valve seat 5. This results in that the compressed air is allowed to flow from the pressure chamber 6 to the output port 4.
However, with the above prior art, there is a possibility of that, if the pressure P of the compressed air Is varied, the force Fp applied to the diaphragm 3 is varied, as shown in FIG. 14, and when the recovering force Fs is larger than the force Fp, the diaphragm 3 is separated from the valve seat 5, resulting in the compressed air being allowed to leak from the output port 4.
The present invention has been provided to solve the above stated problem, being intended to offer a piezoelectric valve with which there is no possibility of the fluid leaking from the pressure chamber with a variation in the pressure of the supplied fluid.